The influence of vibration on the initiation of trees in dielectrics

Polymeric insulation suffers from long-term degradation at low alternating stresses, through the development of tree-like structures of discharge channels emanating from protrusions and inhomogeneities. It can take a considerable time, following the application of voltage, before treeing begins. During this time microscopic voids and cracks form within the dielectric providing the necessary partial discharge activity for treeing to commence. The process leading to the formation of voids and cracks under the influence of low alternating fields has generally been thought to be electronic in nature. The work described in the paper demonstrates that this is not so, and that fatigue failure due to prolonged vibrational electrostatic forces is the cause.